Manchester United must have wished that this truly were a second-rate event. The Premier League club deserved to lose clearly and in the last minute Iker Muniain scored to take Athletic's lead to 3-1 but the hosts reacted with Wayne Rooney converting a penalty. But United were outplayed for much of the Europa League tie.

The side from Bilbao fell 1-0 down yet never seemed perturbed by the fact. So far as the Old Trafford atmosphere was concerned it became one of anxiety. Once Fernando Llorente had put the visitors on level terms the evening fell under the control of Marcelo Bielsa's squad. There was a reminder here that an event of this sort can be much more challenging than a Premier League encounter at this stadium.

There is a hierarchy of honours and some trophies tend to be treated with disdain. In practice, though, clubs will always find themselves being seduced when they start to picture themselves landing a piece of silverware. Liverpool, for instance, did not have to fake delight when they took the Carling Cup this season. By the same token, United are unlikely to snub a prize.

The trouble here was that the visitors gleamed with ambition of their own and it came as a surprise when United went ahead in the 22nd minute after a fine build-up that culminated with Ryan Giggs setting up Rooney to shoot home. All the same, that breakthrough had none of the inevitability associated with United on their own pitch. If anything, the enterprise from Athletic had been more obvious.

Nor did the La Liga side get discouraged and pulled level in the 44th minute, when a patient buildup concluded with Fernando Llorente heading in after a cross by Markel Susaeta from the right of the penalty area. Once snobbery is jettisoned, tournaments all hold some kind of appeal. The Europa League is not just a chore for United, particularly when the opposition have such appetite. The side might have won readily in Amsterdam, but the return at Old Trafford saw Ajax put up a fight before being eliminated in what was ultimately a tense occasion.

Athletic were hardly the sort of club who would capitulate either. They got this far after topping a group in which Paris Saint-Germain were knocked out despite the extraordinary sums poured into the French club by its Qatari owners. There was no cause for anyone in the stands or technical area at Old Trafford to be stifling a yawn over this contest. United are in a gradual transition and this sort of evening had its worth for testing their mettle.

There were saves from David de Gea and all manner of blocks by his team-mates, yet United had a line-up that showed they were entirely in earnest. The selection was far from experimental even if senior figures such as Rio Ferdinand were to be found on the bench. There was sense of Sir Alex Ferguson attempting to calibrate the degree of experience that would leave the club well-placed without making undue demands of a squad whose priority is the Premier League title. It was open to question in those opening 45 minutes whether he had assessed the situation perfectly.

United did have an emphasis on attack. Rooney, for instance, was in the starting line-up that included a specialist finisher in Javier Hernández as well as a winger such as Ashley Young. This, in essence, was a side set up in an almost traditional 4-4-2 system.

Perhaps Bilbao were deemed vulnerable, yet they are a creditable fifth in La Liga. Given the challenge of their domestic scene it seemed improbable that this fixture would disconcert them. Indeed, there was relish to their work. United were unsettled on occasion and might have had a penalty awarded against them when Chris Smalling appeared to tug Fernando Llorente in the 19th minute.

The break of 15 minutes did nothing to snap the visitors' concentration and United were once again compelled to scramble as they defended in a manner that looked increasing preposterous as Athletic performed with vigour and finesse. United were obliged to think primarily on defence and Chris Smalling was withdrawn. Phil Jones retreated into the back four as did Michael Carrick.

The visitors may have wearied just a little and United did not hesitate to make alterations with Anderson introduced for Park Ji-sung. There was some benefit although it also appeared that Athetic had tired themselves with all that pummelling of the hosts in the opening 45 minutes. That seemed to be reflected by a booking for Mikel San José for a foul on Hernández. Muniain had to be denied by De Gea before Athletic moved into a lead they fully merited. Oscar de Marcos scored after an exquisite build-up that released him. United lagged in the tie, but must have known that they had been outplayed for much of the night.